The introduction of hip arthroscopy enabled improved comprehension of this joint and its various pathologies^1,2,3). Interest in hip stability has increased as a result of the increase in indications and number of arthroscopies performed²⁾. Hip stability is dependent upon osseous congruity, the labral suction seal, and the integrity of the hip capsule-ligamentous complex, as well as dynamic muscular forces²⁾. The biomechanics of the native hip can be influenced by an abnormality of one of these anatomical structures²⁾. Microinstability of the hip comprises hip pain accompanied by fine anatomical anomalies⁴⁾. A subtle supra-physiological increased translation of the femoral head occurs in the acetabulum during mobilization of the hip, which can disrupt normal kinematics of the hip, causing symptoms such as hip pain, as well as snapping and/or blocking sensations^2,5). These symptoms are associated with repetitive movements of rotation and axial loading⁴⁾. Finally, this type of instability can lead to changes in hip biomechanics, resulting in development of lesions affecting other anatomical structures such as the labrum, capsule, and cartilage⁴⁾. Reported causes of hip microinstability⁶⁾ include bone anomalies (hip dysplasia and femoro-acetabular impingement), soft tissue pathologies (hyperlaxity, connective tissue disorders) and lesions, trauma, and iatrogenic causes^6,7).

In cases where conservative treatment has failed, surgical management can be considered for treatment of intra-articular lesions as well as eventual associated structural anomalies and to improve hip stability^6,8). In cases where patients do not present with significant osseous anomalies such as severe hip dysplasia, surgical treatment focusing on the capsule-ligamentous complex of the hip has been proposed⁸⁾.

According to our hypothesis, use of arthroscopic capsular plication might result in improvement of short-term clinical and functional outcomes in patients presenting with hip microinstability without gross osseous anomalies. An analysis of operative indications was performed in order to identify the most common presentations of hip microinstability. We also attempted to determine factors that might have a negative influence on postoperative results. Our review of all arthroscopic capsular plication procedures performed at a specialized center was conducted as a preliminary series.

Hip microinstability is a clinical entity that presents as an increased supra-physiological translation of the femoral head in the acetabulum, leading to development of hip symptoms in association with repetitive movements of rotation and axial loading of the hip joint^2,4,5). This condition has been associated with different entities, including hip dysplasia, femoro-acetabular impingement, lesions of intra-articular structures, generalized articular laxity, connective tissue disorders, and trauma^6,7). Diagnosing this pathology is difficult and relies essentially on a high index of suspicion based on medical history, as well as findings from clinical and radiological examinations^4,5,6,7). According to the demographic data from our series, hip microinstability appears to be encountered more frequently in female patients presenting with generalized hyperlaxity or borderline hip dysplasia.

All subjects included in our series were female; however, the predisposition of the female sex for this pathology was not only observed in our series, but has also been reported in other series. All patients who underwent treatment in a series of 31 patients were female⁸⁾. In a second series 81% of patients who underwent treatment were female¹³⁾. Another recently published series reported that 90% of patients were female¹⁴⁾. Some authors have reported that acquired articular hyperlaxity is more common in females^7,15), which could partially account for the female predominance in patients suffering from hip microinstability. In our series seven patients showed signs of generalized hyperlaxity at the initial clinical work-up of which one patient was postoperatively diagnosed with Ehlers–Danlos syndrome. Ehlers–Danlos syndrome might be clinically suspected in patients with a Beighton score ≥5/9 accompanied by elastic skin and some minor criteria such as chronic articular pain¹⁶⁾. In this regard, the Beighton score is an effective, easy-to-use tool for use in the preoperative work-up in cases where hip microinstability is suspected.

An association of hip dysplasia with hip microinstability has also been reported^5,6,7). The original study reported by Wiberg¹⁷⁾ describes hips with a CEA <20° as pathological and hips with a CEA >25° as normal. Hips with CEA between 20° and 25° were considered‘ uncertain’¹⁷⁾. Currently, in the literature on hip arthroscopy, hips presenting with a CEA from 16° to 28° are described as mild or borderline dysplastic, which might cause some confusion¹⁸⁾. Interventions involving periacetabular osteotomy or other acetabular reorientation procedures for treatment of more severe dysplastic hips presenting with a CEA <17° have been associated with high per- and postoperative morbidity^14,18). Some authors have reported that the critical limitation in treatment of dysplastic hips with hip arthroscopy is the fact that underlying osseous structural anomalies cannot be corrected¹⁹⁾. Some findings have suggested the importance of soft tissues in maintenance of hip stability in patients with borderline hip dysplasia, thus arthroscopic capsular plication was introduced as part of the surgical management^8,14). A recent series reported on the results of capsular plication in 21 patients with borderline hip dysplasia with a follow-up period of five years¹⁴⁾. The results showed significant improvement of all functional scores, which was maintained at five years of follow-up and 19% of patients required a revision hip arthroscopy. Another series published in 2017 evaluating capsular plication in 31 hips reported that no significant difference in postoperative improvement was observed between borderline dysplastic hips and non-dysplastic hips⁸⁾. Another series comparing the effects of capsular plication between patients presenting with borderline hip dysplasia and patients presenting with ligamentous hyperlaxity also reported that there was no significant difference¹³⁾. The results of our series, which also compared postoperative improvement of functional scores between patients with dysplastic hips and those with non-dysplastic hips, showed no significant difference (P>0.05). However, in our analysis of the failure rate of this intervention (23.1% or six patients), which included patients who benefitted from a periacetabular osteotomy and those who were not satisfied, we observed that five of these six patients also presented with a lateral CEA ≤25°. In addition, it should be noted that the four patients who benefitted from a revision with a periacetabular osteotomy were not included for this end point analysis at final follow-up, thus weakening the significance of these results.

A study describing the femoro-epiphyseal acetabular roof or FEAR index was recently published¹¹⁾. This index is represented by an angle between the mid-third of the epiphyseal line of the femoral head and the acetabular roof. An angle directed medially is negative and considered stable while an angle with an external direction is positive representing external directed forces favoring translation of the femoral head. Using this index, in cases of borderline dysplasia, identification of stable hips from unstable hips with a sensitivity of 80% and a specificity of 78% was reported¹¹⁾. According to our findings, five hips presented with a positive FEAR index. All of these hips presented with a lateral CEA ≤21°. Of these five hips, four hips benefitted from a periacetabular osteotomy to address failed arthroscopic management of hip microinstability. Of the two remaining patients, one patient was lost to follow-up and one patient had a follow-up period of less than 12 months and therefore was not included for the final evaluation. Because our series included only a small number of hips, we can only suggest that the FEAR index should be utilized in larger series in order to confirm its role in identifying borderline dysplastic hips that might not benefit from arthroscopic treatment.

Although maintenance of significant improvement in functional scores has been demonstrated in all series reported in the literature^8,13,14,16), sports activities appear to be of less importance. Two series evaluating the Hip Outcome Score – Sport Specific Subscale reported significant improvement of this score after arthroscopic capsular plication^13,14). However, there are no detailed reports with regard to sports activities and rates of return to participation in sports. In our opinion these details are of uttermost importance in this young and active population. Our series showed good results with significant improvement in WOMAC scores with mean improvement of 47.2 points and mean patient satisfaction of 7.7/10. However, only 46% of recreational sportive patients actually returned to their preferred sporting activities and only one patient was able to perform at the same level as before the development of symptoms, downgrading these‘good results’.

We acknowledge that because the technique of capsular plication has not yet been standardized and is dependent upon the capsulotomy technique performed when accessing the hip during arthroscopy, comparison between different series is difficult²⁰⁾. In addition, evaluating the effect of the plication itself is also difficult since management of hip microinstability must include treatment of all associated lesions^8,13,14).

The limitations of this study must be considered due to its retrospective design and small case series. Because only 26 hips were included for evaluation at final follow-up, demonstrating any difference in postoperative evolution between groups is difficult due to lack of power. The WOMAC score was used in our study because we only had a preoperative WOMAC score and the WOMAC score has been validated for use in survey evaluation. However, in our opinion this tool might not represent the best outcome score for evaluation of young and active patients.

Microinstability of the hip remains a continuously evolving and complex pathology. Management of this pathology with arthroscopic capsular plication results in short-term improvement of pain and functional scores in carefully selected patients. Conduct of further study will be required in order to evaluate the role of new parameters, including the FEAR index, in the surgical decision-making process. Conduct of long-term studies will be required in order to clarify the role of capsular plication in the arthroscopic management of hip microinstability.

Front view of a right hip representing the sutures of the capsular plication along the borders of the previously performed longitudinal capsulotomy.

Arthroscopic view of anchor placement for proximal suture point.

Box plot representation of the pre- and postoperative WOMAC scores.

Preop: preoperative, Postop: postoperative, WOMAC: Western Ontario and McMaster Universities Osteoarthritis.